The present invention relates to an polymerized and labelled antibody prepared by polymerizing an antibody and binding the resultant polymerized antibody to a protein to form a protein complex or polymerized antibody conjugate, and labelling the conjugate with a cyanine dye, and further to a method for manufacturing the same.
A dye-labelled antibody prepared by labelling an antibody with a dye, which is visible optically, has a specific reaction with an immunogen or antigen contained in a sample solution. Therefore, such antibody has been used, for example, in an immunosensor for detecting a specific substance or antigen contained in a sample solution with the aid of immunological antigen-antibody reaction and has a wide application as a diagnostic means at various medical facilities.
Cyanine dyes are the most frequently used dyes for labelling antibodies, because they are highly reactive and have a high molar absorption coefficient (see Bioconjugate Chemistry Vol. 4, No. 2, pp. 105-111, 1993).
Those cyanine dyes have a functional group which reacts with an amino group or a carboxyl group present in the antibody and forms a covalent bond. The binding ratio of cyanine dye to antibody is 20 to 50 molecules per molecule of antibody.
The cyanine dye-labelled antibody thus produced has been applied to, for example, immunochromatography because of its generally high visibility and widely used for detecting a small amount of a specific substance such as human chorionic gonadotropin which is contained only in the urine of pregnant women.
Normal antibody includes several hundreds to several thousands of amino group or carboxyl group. However, the conventional interpretation is that, of those many amino or carboxyl groups, only 50 or so can participate in the reaction due to its three-dimensional structure, which limits the number of binding molecules of cyanine dye to 50 molecules per molecule of antibody.
Moreover, since the antibody has a limited number of reaction site with antigen only to 2 for one molecule, the binding sensitivity of antibody to antigen remains low.
The use of such a labelled antibody in an immunosensor or the like limits the sensitivity of the sensor, producing a significant problem of difficult detection of analyte, that is, antigen if its concentration in a sample solution is low.
In view of the above-mentioned problems, the object of the present invention is to provide a high-sensitive indirect polymerized and labelled antibody facilitating detection of a low concentration of analyte in a sample solution.
Another object of the present invention is to provide a method for manufacturing the polymerized and labelled antibody as stated above.